Recommendation Letters from Alumni more helpful to my application?

Hi there - great question ! Cornell requires 2 teacher rec letters and 1 counselor one, so it's unlikely that this Cornell alum you know would be eligible to write you a letter anyways, unless they were your teacher (see application requirements here: https://admissions.cornell.edu/apply/first-year-applicants/admissions-requirements). Some schools do allow an additional rec letter, but it's not recommended to send anything extra unless it reveals something truly important that couldn't be shared in the rest of your application. This is because admissions officers have so many apps to review already, so if they get something extra that doesn't really add to your application, they often are unhappy and may view you unfavorably.

Regardless of the requirements, however, admissions committees care less about who the recommender is and more about their relationship to you. It's more important to find a recommender who knows you well and has a lot of good things to say about you, rather than someone who's powerful, famous, or connected to the school. You asked if the rec letter would help if it were from a Cornell alum, even if the level of the letter were the same - the truth is, a letter from the standard alum won't make a difference. If the alum is really important to Cornell (maybe has donated a ton of money, has a building named after them, etc), then their rec letter might give you a boost, but again only the alum knows you very well personally.

Here's a CollegeVine article that has more info about alumni & famous person rec letters: https://blog.collegevine.com/will-getting-a-letter-from-an-alumnus-famous-person-or-government-official-boost-my-chances/